Common video output interfaces include a YPbPr interface (e.g., a color difference component interface, which is divided into three channels that respectively transmit a Y signal (luminance signal), a Pb signal (analog component blue color difference signal), and a Pr signal (analog component red color difference signal)), a YC interface (e.g., an S-Video interface (luminance separation interface), which is divided into two channels that respectively transmit a Y signal (luminance signal) and a C signal (color signal)), and a CVBS (composite video broadcast signal) interface. The YPbPr interface needs three video digital-to-analog converters (DACs) to respectively transmit the Y signal, Pb signal, and Pr signal, the YC interface needs two video DACs to respectively transmit the Y signal and C signal, and the CVBS interface needs one video DAC to transmit the CVBS signal.
To lower the cost and power consumption, the number of video DAC ports provided externally by a main chip of an existing set-top box is reduced from 6 originally to 3 or 4. To use 3 or 4 video DAC ports to implement the three video output interface modes, the set-top box needs to know a type of a required video signal to help dynamically adjust the output signal format of the video DAC, implementing the corresponding video output interface mode. In the prior art, the type of video signal to be output may be known in the following two ways:
(1) The YPbPr interface mode, YC interface mode, and CVBS interface mode are configured in the set-top box. A user controls the set-top box through a control panel or remote control to switch between the three interface modes, selects the video output interface mode that matches the currently connected television load terminal, and thereby notifies the set-top box through the control panel or remote control of the type of video signal to be output. However, this implementation method requires participation and operation of the user, and has the drawback of failing to automatically identify the type of video signal to be output, lowering service quality for the user.
(2) The set-top box uses a customized terminal socket. This socket has an embedded identification pin. The one or multiple video DAC ports that are connected to the load terminal are identified through this pin, and thereby the type of video signal corresponding to the required video output interface mode is known. The disadvantage of this implementation way is that the design structure of the terminal socket is complicated, and the hardware implementation cost is high.